Process for preparing a synthetic fuel from solid, combustible materials

ABSTRACT

The invention is directed to a process for preparing a synthetic fuel from solid, combustible materials by treating these materials with a water-redispersible polymer powder composition.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a process for preparing a synthetic fuel from solid, combustible materials by treating these materials with a water-redispersible polymer powder composition.

2. Background Art

A synthetic fuel is a material which is generated by the conversion of natural fuel materials, like coal, crude oil, natural gas or wood. Basically there are two mechanism of conversion-degradation processes and chemical reactions. Degradation processes are well-known in the state of art. Typical examples of synthetic fuel prepared by a degradation process are synthetic oil or synthetic gas produced from coal, synthetic gas produced from wood, and synthetic oil produced from crude oil. Typical examples of synthetic fuel prepared by chemical reactions are fuel materials obtained by acylation or alkylation of coal with organic chemicals.

Usually the synthetic fuel materials are used for heating, for examples in power plants for district-wide heating, in plants for electric power generation, and for the production of coke.

U.S. Pat. No. 6,641,624 B1 claims a process of preparing synthetic fuel from coal, by preparing a mixture of coal with an aqueous polymer solution or an aqueous polymer emulsion, and a glycol or glycerin diluent as the third component. In comparison with the above mentioned methods this process has the advantage of improved environmental acceptability. But it has the disadvantage, that with aqueous solutions or emulsions, a high amount of water is introduced. Typically an aqueous polymer emulsion has a solids content of about 50%, the remainder being water. This large amount of water must then be removed in order not to cause a dramatic reduction of the BTU value of the synthetic fuel. In the method of the U.S. Pat. No. 6,641,624 water is used to the extent of 1.5 to 2.5 times higher than the amount of coal by weight. The cost of the diluent also renders the process less attractive economically.

SUMMARY OF THE INVENTION

An object of the invention is to provide a method of preparing a synthetic fuel from solid, combustible materials and polymer materials, which can be processed in common synthetic fuel plant equipment, and which does not have the disadvantage of introducing a high amount of non-combustible materials like water into the fuel. These and other objects are achieved through the addition of a water-redispersible polymer powder to solid, combustible fuel components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The invention is thus directed to a process for preparing a synthetic fuel from solid, combustible materials by treating these materials with a water-redispersible polymer powder composition.

Preferred solid, combustible materials are coal, for example anthracite, bitumen or lignite. Preferred too is wood, for example in the form of wood chips or saw dust. Waste plastic materials may also be used in this process as a solid, combustible material. The solid combustible material may therefore be selected from any variety of combustible solids, either alone or in a myriad of mixtures.

Redispersible polymer powders are characterized in that they are readily redispersible after stirring with water, largely breaking down into particles substantially indistinguishable from those of the initial dispersions from which the powders are prepared, and which react or associate with certain organic materials. Redispersible polymer powders are commercially available from Wacker Polymer Systems under the trademark Vinnapas®. The polymers are preferably based on one or more monomers from the group of vinyl esters, (meth)acrylates, vinyl aromatics, olefins, 1,3-dienes and vinyl halides and, if required, further monomers copolymerizable therewith.

Suitable vinyl esters are those of carboxylic acids having 1 to 12 C atoms. Vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate, vinyl pivalate and vinyl esters of a-branched monocarboxylic acids having 9 to 11 C atoms, for example VeoVa9^(R) or VeoVa10^(R) (trade names of Resolution Products), are preferred. Vinyl acetate is particularly preferred.

Suitable monomers from among the acrylates and methacrylates are esters of straight-chain or branched alcohols having 1 to 15 carbon atoms with acrylic acid or methacrylic acid. Preferred methacrylates and acrylates are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate and 2-ethylhexyl acrylate. Methyl acrylate, methyl methacrylate, n-butyl acrylate, tert-butyl acrylate and 2-ethylhexyl acrylate are particularly preferred. Preferred vinyl aromatics are styrene, methylstyrene and vinyltoluene. A preferred vinyl halide is vinyl chloride. The preferred olefins are ethylene and propylene, and the preferred dienes are 1,3-butadiene and isoprene.

If required, 0.1 to 5% by weight, based on the total weight of the copolymer, of auxiliary monomers may also be copolymerized, preferably, 0.5 to 2.5% by weight. Examples of auxiliary monomers are ethylenically unsaturated mono- and dicarboxylic acids, preferably acrylic acid, methacrylic acid; ethylenically unsaturated carboxamides and carbonitriles, preferably acrylamide and acrylonitrile; and ethylenically unsaturated sulfonic acids and their salts, preferably vinyl sulfonic acid and 2-acrylamido-2-methylpropane sulfonic acid. Further examples are precrosslinking co-monomers such as polyethylenically unsaturated comonomers, for example divinyl adipate or triallyl cyanurate, or postcrosslinking comonomers, for example N-methylolacrylamide (NMA), N-methylolmethacrylamide, alkyl ethers, such as the isobutoxy ether, or esters, of N-methylolacrylamide. Comonomers having epoxide functional groups, such as glycidyl methacrylate and glycidyl acrylate, are also suitable. Further examples are comonomers having silicon-containing functional groups, such as (meth)acryloyloxypropyltri(alkoxy)silanes, vinyltrialkoxysilanes and vinylmethyldialkoxysilanes.

The choice of monomers or the choice of the amounts by weight of the comonomers is made in such a way that in general a glass transition temperature (Tg) of −50° C. to +50° C., preferably −30° C. to +40° C., and most preferably −5° C. to +15° C., is obtained. The glass transition temperature Tg of the polymer can be determined in a known manner by means of differential scanning calorimetry (DSC). The Tg can also be calculated approximately beforehand using the Fox equation. According to T. G. Fox, BULL. AM. PHYSICS SOC. 1, 3, page 123 (1956), the following is applicable: 1/Tg=x₁/Tg₁+x₂/Tg₂+ . . . +x_(n)/Tg_(n), where x_(n) is the mass fraction (% by weight/100) of the monomer n and Tg_(n) is the glass transition temperature in Kelvin of the homopolymer of the monomer n. Tg values for homopolymers appear in POLYMER HANDBOOK, 2nd Edition, J. Wiley & Sons, New York (1975).

Particularly preferred are vinyl acetate homopolymers, copolymers of vinyl acetate with ethylene, copolymers of vinyl acetate with ethylene and with one or more other vinyl esters, copolymers of vinyl acetate with ethylene and (meth)acrylic ester(s), copolymers of vinyl acetate with (meth)acrylates and other vinyl esters, copolymers of vinyl acetate with ethylene and vinyl chloride, copolymers of vinyl acetate with acrylates, styrene-acrylic ester copolymers, and styrene-1,3-butadiene copolymers, it being possible for these polymers also containing, if required, one or more of the above-mentioned auxiliary monomers.

The polymers are prepared by methods well known to those skilled in the art, for example by emulsion polymerization or suspension polymerization. The thus obtained initial polymer dispersions preferably have a solids content of 30 to 70%. For the preparation of the water-redispersible polymer powders, the aqueous dispersions are preferably spray-dried, usually after the addition of protective colloids as spraying assistants. Common additives which may also be incorporated in the water-redispersible polymer powders are anti-blocking agents.

In the production of synthetic fuel materials based on solid, combustible materials, the common process steps are in general as follows: The solid, combustible material is delivered to a place where the reaction between the combustible material and the polymer component takes place. Typically the solid, combustible material is transported on a conveyor belt to the reaction region. In the reaction section of the plant the polymer is added to the combustible material in a manner to ensure the reaction between the solid, combustible material and the polymer component. From the reaction section the synthetic fuel thus produced is transported to a place for storage or is directly transported to a combustion section.

In general the solid, combustible material is reacted with 0.01 to 10% by weight, preferably 0.1 to 5% by weight of the redispersible polymer powder, based on the weight of the solid combustible material. The reaction between the solid, combustible material and the redispersible polymer powder usually takes place at a temperature between 5° C. to 70° C., preferably 15° C. to 30° C. Preferably the reaction takes place under normal atmospheric pressure.

The present process can be designed as a dry process or a wet process:

In a first embodiment of the dry process the redispersible polymer powder composition is metered onto the combustible material, preferably by dusting the powder onto the combustible material on the conveyor belt. The mixture of combustible material and redispersible polymer powder continues along the conveyor, and in a preferred embodiment it is treated with water or steam. Usually 0.1% by weight to 50% by weight, preferably 0.1% to 10%, and most preferably 0.1% to 2% of water or steam are contacted with the mixture of combustible material and polymer powder just before entering a mill, the amounts by weight based on the weight of combustible material. In each embodiment of the present process the water is only needed to improve the contact between the combustible material and the polymer. The amount of water also depends on the moisture content of the combustible material. Therefore depending on the glass transition temperature of the polymer and the moisture of the combustible material, in general only very low amounts of water need to be added, in contrast to prior art processes, where the water is primarily needed to transport the polymer to the coal, and therefore very high amounts are required. In this first embodiment, the thus treated mixture of combustible material and redispersible polymer powder continues along the conveyor and into the mill where they are thoroughly mixed.

In a second embodiment the solid, combustible material is also transported along the conveyor, and is treated with water or steam in the above mentioned amounts. The redispersible polymer powder is then metered onto the coal carrying conveyor just before entering the mill, where the combustible material and polymer are thoroughly mixed.

In a third embodiment of the dry process the redispersible polymer powder composition is metered onto the combustible material, preferably by dusting the powder onto the combustible material on the conveyor belt. The mixture of combustible material and redispersible polymer powder continues along the conveyor and into the mill where mixing begins to take place. Within the mill, water or steam in an amount as described above is introduced.

In a fourth embodiment the redispersible polymer powder composition is metered onto the combustible material, preferably by dusting the powder onto the combustible material on the conveyor belt. The mixture of combustible material and redispersible polymer powder continues along the conveyor and into the mill where they are thoroughly mixed. When the material exits the mill, the material passes a unit where it is treated with water or steam in an amount as described above.

In a wet process design, the solid, combustible material proceeds along the conveyor and is sprayed with an aqueous redispersion of the redispersible polymer before entering the mill, where the combustible material and polymer are thoroughly mixed. The redispersion is prepared by admixing redispersible polymer powder with water. In a further embodiment of the invention, the solid, combustible material proceeds along the conveyor, and enters the mill, wherein an aqueous redispersion of the redispersible polymer is added. The mixture is thoroughly mixed in the mill. In both these embodiments, organic diluents such as glycols, glycerine, etc. are preferably absent.

In general the milling step is followed by a consolidation step, such as briquetting.

The reaction between the solid, combustible material and the polymer takes place substantially in the milling step at the above defined conditions. The reaction is controlled by analytical methods well-known for this purpose in the state of art. Preferred are Fourier-transform infrared spectroscopy (FTIR) and the thermogravimetric analysis (TGA). The procedures are known to those skilled in the art, as indicated by U.S. Pat. No. 6,641,624, column 6, line 34 to column 8, line 60, herein incorporated by reference.

The inventive process reduces the complexity of raw material procurement logistics, because of the solid state of the polymer. Flat-bed transport is more economical to the end user than liquid bulk transport. At low temperatures, freezing generally destroys aqueous polymer dispersions, but does not affect redispersible polymer powders, thus not requiring the addition of diluent. The dry process allows the customer to utilize less polymer based on the fact that reaction kinetics are closely linked with proximity of reactants. Using redispersible polymer powder, the extra step required on current state of the art, i.e. diluting the aqueous polymer emulsion, is removed. Above all, the amount of water used in the process, which is detrimental to the end product, is minimized in comparison to the state of the art.

EXAMPLES

In examples 1 to 3 a water-redispersible polymer powder composition based on a vinyl acetate ethylene copolymer with a glass transition temperature Tg of −7° C. was used. In examples 5 to 7 a water-redispersible polymer powder composition based on a vinyl acetate homopolymer with a glass transition temperature Tg of +30° C. is used.

Example 1

1000 g of coal fines are introduced into a blender and dry-mixed with 10 g of water-redispersible polymer powder. The mix is spread out onto a metal plate and uniformly sprayed with 100 ml of water. Agglomeration of the coal fines occurs.

Example 2

1000 g of coal fines are sprayed with steam until a weight increase of 5% is measured. The wet coal fines are introduced into a blender and mixed with 10 g of water-redispersible polymer powder. Agglomeration of the coal fines occurs.

Example 3

1000 g of coal fines is sprayed with 100 g of an aqueous redispersion of the water-redispersible polymer powder with a solids content of 50%. The wet coal fines are introduced into a blender and mixed. Agglomeration of the coal fines occurs.

Comparison Example 4

1000 g of coal fines are mixed with 10 kg of a polymer dispersion based on a vinyl acetate ethylene copolymer (Tg=−7° C.) with a solids content of 50%. A dispersion with a syrup-like consistency is obtained.

Example 5

The procedure of Example 1 is followed with the exception that a water-redispersible polymer powder composition based on a vinyl acetate homopolymer with a glass transition temperature Tg of +30° C. is used. Agglomeration of the coal fines occurs in the same manner.

Example 6

The process of Example 2 is followed with the exception that a water-redispersible polymer powder composition based on a vinyl acetate homopolymer with a glass transition temperature Tg of +30° C. is used. Agglomeration of the coal fines occurs in the same manner.

Example 7

The process of Example 3 is followed, on the exception that a water-redispersible polymer powder composition based on a vinyl acetate homopolymer with a glass transition temperature Tg of +30° C. was used. Agglomeration of the coal fines occurs in the same manner.

The comparison between the examples and the comparison example shows that in contrast to state of the art procedures, with the inventive process a synthetic fuel in a solid state is obtained, ready for combustion, without loss in heat energy owing to the necessity to evaporate a high amounts of water.

In the context of the invention, and also in the claims, where water or steam is specified, a mixture of water and steam may of course be used. By the term “along a conveyor” or “on a conveyor” is meant transport over a distance irrespective of the actual construction of the conveying means. In most instances, a conveying belt, either continuous or of links, etc., may be used. However, other conveying means such as screw-type conveyors, bucket-type conveyors, pneumatic tube conveyors, and like or equivalent conveying means, i.e. any suitable means may be used.

While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. 

1. A process for preparing a synthetic fuel from solid, combustible materials, comprising treating the combustible materials with a water-redispersible polymer powder composition.
 2. The process of claim 1, wherein the solid, combustible material is selected from the group consisting of coal, wood, and waste plastic materials.
 3. The process of claim 1, wherein the water-redispersible polymer powder is based on one or more monomers selected from the group consisting of vinyl esters, (meth)acrylates, vinyl aromatics, olefins, 1,3-dienes and vinyl halides and, if required, further monomers copolymerizable therewith.
 4. The process of claim 1, wherein the water-redispersible polymer powder comprises one or more polymers selected from the group consisting of homopolymers and copolymers of vinyl ester monomers; copolymers of vinyl acetate and ethylene; copolymers comprising vinyl acetate, ethylene and a vinylester of at least one a-branched monocarboxylic acids having 9 to 11 C atoms, said homopolymers and copolymers optionally containing one or more auxiliary monomers.
 5. The process of claim 1, wherein the redispersible polymer powder composition is metered onto the combustible material in dry form, the mixture of combustible material and redispersible polymer powder is transported along a conveyor, and is treated with water or steam before entering a mill, where the combustible material and polymer are thoroughly mixed.
 6. The process of claim 1, wherein the solid, combustible material is transported along a conveyor, is treated with water or steam, and subsequently a redispersible polymer powder is metered onto the coal carrying conveyor just before entering a mill, where the combustible material and polymer are thoroughly mixed.
 7. The process of claim 1, wherein the redispersible polymer powder composition is metered onto the combustible material, and the mixture of combustible material and redispersible polymer powder is transported along a conveyor and a the mill where the combustible material and polymer powder are thoroughly mixed, and water or steam is introduced.
 8. The process of claim 1, wherein the redispersible polymer powder composition is metered onto the combustible material, and the mixture of combustible material and redispersible polymer powder is transported along a conveyor and into a mill where the combustible material and polymer powder are thoroughly mixed, and after the material exits the mill, the mixture is treated with water or steam.
 9. The process of claim 1, wherein the solid, combustible material proceeds along a conveyor and is sprayed with an aqueous redispersion of the redispersible polymer before entering a mill, where the combustible material and redispersible polymer are thoroughly mixed.
 10. The process of claim 1, wherein the solid, combustible material proceeds along a conveyor and is enters a mill, where an aqueous redispersion of the redispersible polymer is added, and the mixture is thoroughly mixed in the mill.
 11. The process of claim 1, further comprising forming the mixture of redispersible polymer powder and combustible material into briquettes. 